Environmental contamination is a severe problem endangering the lives of many plants and animals, including humans. Many attempts are being made to reduce contamination by either preventing escape of the contaminants into the environment, containing the contaminants, or treating the contaminants in some way to make them less harmful. However, the first step in contaminant elimination or reduction is the identification of the contaminant followed by a determination of the quantity of contamination at the contaminated site. As the contaminated site is treated, such as by contaminant removal, degradation or encapsulation, the site is monitored to determine the effectiveness of the clean-up procedure.
The current approach of collecting soil and water samples and sending them to a laboratory for chemical analysis is time-consuming, inefficient, costly, may result in inaccurate measurements, and can pose health and safety risks to workers and the community. Ideally, the degree of contamination remaining in a contaminated site during and after the clean-up procedure should be monitored by personnel at the site. For example, during a remediation effort involving large, expensive earth moving equipment, it is important to know whether all of the contaminated soil has been removed from a site before equipment and personnel are moved to the next job site. Immediate results regarding the extent of remaining contamination allow these decisions to be made in the most cost effective manner. To be effective in the field, contaminant monitoring methods must be simple, portable, rapid, unambiguous, able to withstand harsh environmental conditions, and should provide results that can be visualized at the test site, preferably in the absence of instrumentation.
A major component of the costs associated with a hazardous site characterization can be attributed to analytical testing. Gas chromatography (GC) and gas chromatography/mass spectroscopy (GC/MS) are common analytical methods utilized to evaluate environmental pollutants. Although highly sensitive, these methods require sophisticated equipment that are not easily adapted for use in the field. Portable gas chromatograph/mass spectrometers (GC/MS) for sample analysis in the field have been developed. However, the costs of production, maintenance, and operation of such instruments by highly trained technicians are understandably high.
Halogenated Hydrocarbons
Halogenated hydrocarbons have been identified as common pollutants in the United States. Halogenated hydrocarbons have been and still are widely used in many industries as cleaning solvents, refrigerants, fumigants, and starting materials for the syntheses of other chemicals. This class of contaminants includes volatile halogenated hydrocarbons, such as trichloroethylene, a general solvent and degreaser and the most prevalent halogenated hydrocarbon contaminant, and perchloroethylene (dry cleaning fluid). Because of the extensive use and stability of halogenated hydrocarbons, hundreds of contaminated groundwater and landfill sites exist in the United States.
Trichloroethylene (TCE) is a volatile compound, routinely used as a solvent in various industrial applications throughout the world. Because of its prevalent use, frequent releases of this compound from accidental spills, leaking storage containers and improper disposal practices have led to environmental contamination. Due to its potential teratogenic, mutagenic and carcinogenic properties coupled with a partition coefficient that suggests its ability to migrate quickly through soil, federal regulations have been enacted to limit trichloroethylene levels in the environment.
To determine if trichloroethylene contamination exists, an accurate and reliable site characterization must be performed. The extent of the contamination is determined by making borings at regular intervals across the entire site and taking samples from each boring every two to five feet until the water table is encountered. Trichloroethylene levels in these samples are used to project the extent of the contaminant plume. Because of the volatility associated with trichloroethylene, special sample collection, handling and storage techniques must be employed to minimize contaminant loss to evaporation and assure accuracy from the analysis. When dealing with volatile compounds, such as trichloroethylene, the most accurate and reliable results are usually obtained from on-site testing or 24 hour turn-around analyses.
Immunoassays
Various approaches have been described for carrying out immunoassays (e.g. P. Tijssen, PRACTICE AND THEORY OF ENZYME IMMUNOASSAYS, Elsevier, Amsterdam, 1985), which rely on the binding of analyte by an analyte receptor or antibody to determine the concentrations of analyte in a sample. The most widely applied immunoassay method for detection of small molecules, such as those having a molecular weight less than 1000 daltons, is the heterogeneous, competitive immunoassay. In the heterogeneous, competition immunoassay a structurally similar derivative or analog of the analyte to be detected is chemically coupled to a substance to form an analyte-conjugate. The analyte-conjugate is employed as a reagent in the assay and competes with analyte in the sample for antibody binding sites. Either the antibody or the analyte-conjugate is labeled in such a way as to render them detectable, and the immunoassay method provides a physical means for separating bound and unbound label. A sample suspected of containing analyte, the analyte-conjugate, and the antibody are reacted together. Bound and unbound label are separated and either can be quantitated as a measure of analyte concentration in the sample.
Environmental Immunoassays
Immunoassay methods have been available for the detection of some environmental contaminants for several years. However, a crucial step in the development of an immunoassay is the availability or production of antibodies that bind to the analyte to be detected. Small molecules such as trichloroethylene (ClCHCCl.sub.2) and perchloroethylene (C.sub.2 Cl.sub.4) are too small to produce an appropriate immune response when injected into laboratory animals. Such molecules, commonly referred to as haptens, must first be coupled to a larger molecule, commonly referred to as a carrier molecule, to produce a conjugate that then may be used to produce antibodies. However, the ability to produce antibodies to hapten is not predictable. Furthermore, even if antibodies to the hapten are produced, they may not possess sufficient sensitivity and specificity for the analyte to be utilized in an immunoassay having the requisite performance characteristics.
Antibodies for use in an immunoassay for the detection of small aliphatic organic compounds including trichloroethylene and perchloroethylene are available as described in U.S. Pat. No. 5,273,909 to Roger Piasio. However, these antibodies react better with other organic compounds such as toluene and therefore lack specificity for trichloroethylene.
Little progress on the development of inexpensive, onsite monitoring methods, such as immunoassay methods, has been made. Therefore, there is an on-going need for development of antibodies and immunoassays specific for the detection of trichloroethylene and perchloroethylene, particularly assays that are highly sensitive and specific, and can be used for on-site detection of environmental contamination.